An assumption is a proposition that is taken for granted, in other words, that is treated for the sake of a given discussion as if it were known to be true.

There are two levels of assumption that make reasoned scientific debate problematic.

The first is where there is a basic premise in an argument which is not shared by the discussants. Take for example the notion of spiritual energy which underpins the psychological theories of much of the world. If we do not believe it exists we cannot enter into a debate about an aspect of its operation, we simply do not share the basic assumption on which the edifice is built.

The second case is where we share a belief in the importance of an underlying premise, but where we differ on the understanding of the terms. The essentially contested concept make progress in the argument difficult.

In logic, more specifically in the context of natural deduction systems, an assumption is made in the expectation that it will be discharged in due course via a separate argument.